The present invention relates to a molded plastic container or bucket and a compatible lid wherein the lid is removably secured to the open end of the container.
Many designs of molded plastic buckets or containers are known, for example, as disclosed in the following patents of John W. Von Holdt, Sr.: U.S. Pat. Nos. 4,375,948; 4,574,974; 4,512,494; 4,512,493; 4,452,382; 4,380,305; 4,308,970; and 4,210,258. Buckets or containers for food, paint, solvents and chemicals have been made from molded plastic materials in accord with the teachings of such patents. However, molded plastic buckets may lack the strength of buckets fabricated from metal. Thus special designs for plastic buckets may be adopted to obtain, for example, desired structural integrity, hoop strength and stacking strength. Hoop strength relates to the function or characteristic of the container to resist lateral deformation or change in the cross sectional shape of the container when lateral forces act upon the sides of the container. Stacking strength relates to the function or characteristic of the container to support vertical loads such as those which may occur when containers are stacked upon each other.
Also the design of the mouth or open end of a plastic bucket or container and a compatible lid presents a challenge to provide a lid that is properly retained and sealed on the open top of the bucket. Von Holdt in U.S. Pat. No. 5,538,154 entitled Snap-On Flexible Lid discloses a plastic lid with a peripheral flange constructed to enhance the “drop strength” of the lid while retaining flexibility adequate to permit removal of the lid from a container. Drop strength relates to the function or characteristic of the lid to maintain attachment to a container even when dropped from various heights. Von Holdt in U.S. Pat. No. 5,437,386 entitled Container with Tamper-Evident Lid Removal Means discloses additional embodiments of compatible molded plastic bucket and lid constructions.
Attachment of a lid to the open end of a molded plastic bucket often involves frictional or interference engagement or interaction between a rib, lip or groove molded in the open end of the bucket and a circumferential flange projection or groove in the lid. For example, the lid may include a radially, inwardly extending flange, rib or lip that is engaged with an outwardly extending rib on the outside wall of the bucket. A typical prior art lid and bucket combination is depicted in the cross section in FIG. 1. A bucket side wall 10 includes two circumferential, outwardly extending radial ribs 12, 14 which are each cooperative with a separate, inwardly extending circumferential, radial flange, 18, 20 on a skirt 13 of the lid 11. Flanges 18, 20 fit over the bucket ribs 12, 14 and thereby hold or retain the lid 11 on the bucket. The flanges 18, 20 resist release or removal of the lid 11 from the top or open end of the bucket.
Such prior art constructions work well. However, the need for a tamper resistant, improved lid construction for use in combination with a molded plastic bucket has remained.